Most previous investigations of central respiratory nuclei have been designed to examine the rhythmogenic functions of respiratory modulated neurons in the dorsal (DRG) and ventral (VRG) respiratory groups. However, since respiratory timing is not altered by destruction of more than 80% of the DRG-VRG neurons, it appears likely that the respiratory rhythm is generated at a site outside these regions. These results, when combined with other recent data, suggest that the role of the DRG and VRG may be to integrate afferent feedback with the basic feedforward timing signal which is determined elsewhere. Sinc;e the concept of respiratory rhythmogenesis at a side outside the DRG-VRG is of such fundamental importance, it deserves further study. In one of the proposed projects the results of a previous microlesion study performed by Speck and Feldman will be re-examined. Both the inspiratory and expiratory modulated regions of the DRG and VRG will be lesioned in decerebrate cats. Therefore, in addition to re-examining the results of the previous study, these experiments will provide new information by determining the necessity of the caudal VRG and forebrain structures for respiratory rhythmogenesis. Another proposed project will determine the relative contribution of vagal and pontine afferents in the termination of inspiration. Intercostal nerve stimulation will be used as a technique to assess the threshold for inspiratory termination in decerebrate cats. After determination of the control thresholds, inspiratory termination will be examined while the vagus nerves are bilaterally cold blocked, then after bilateral pontine lesions. The third project is designed to examine the central projections of phrenic afferents. Brainstem microelectrode recording will be used to map the DRG and VRG for both field potentials and evoked neuronal activity elicited by electrical stimulation of the phrenic nerve. Later experiments will attempt to identify the receptors and physiologic significance of these phrenic afferent reflexes.